1. Field of the Invention
The present invention relates to a solvent-assisted lithographic process for depositing ridge waveguides on substrates utilizing simple photomask technology and photosensitive sol-gel wave-propagating material.
In the present disclosure and the appended claims, the term "ridge waveguides" is intended to designate not only ridge waveguides but other devices such as splitters and directional couplers made of ridge waveguides.
2. Brief Description of the Prior Art
Ridge waveguides are basic building block structures for integrated optic devices and components. Ridge waveguides are conventionally fabricated out of glass by multi-step combinations of lithographic photomask technologies and etching processes which utilize equipments, for example reactive ion etchers, requiring a substantial capital investment and infrastructure. Moreover, ridge waveguides structures are fabricated from glass that must match the refractive index and other characteristics of optical fibers to be attractive to the photonics industry.
The prior art technologies for fabricating glass integrated optic devices and components comprise:
sputtering; PA1 thermal oxidation; PA1 chemical vapor deposition; PA1 plasma enhanced chemical vapor deposition; PA1 flame hydrolytic deposition; and PA1 sol-gel deposition. PA1 mixing methacryloxypropyltrimethoxysilane (H.sub.2 C.dbd.C(CH.sub.3)CO.sub.2 (CH.sub.2).sub.3 Si(OCH.sub.3).sub.3) with 0.01M HCl in a molar ratio of 1:0.75 to produce a first mixture; PA1 mixing zirconium(IV)-n-propoxide (Zr(OC.sub.3 H.sub.7).sub.4), referred to in the present disclosure and in the appended claims to as Zr(OPr).sub.4, with n-propanol in a volume ratio of 1:1 to produce a second mixture, and adding to this second mixture 1 mole of methacrylic acid (H.sub.2 C.dbd.C(CH.sub.3)COOH) by mole of Zr(OPr).sub.4 to produce a third mixture; PA1 mixing the first and third mixtures to produce a fourth mixture containing methacryloxypropyltrimethoxysilane (H.sub.2 C.dbd.C(CH.sub.3)CO.sub.2 (CH.sub.2).sub.3 Si(OCH.sub.3).sub.3) and Zr(OPr).sub.4 in a molar ratio of 4:1; PA1 mixing the fourth mixture and deionized water (H.sub.2 O) to obtain a fifth mixture in which the molar ratio of deionised water (H.sub.2 O) to Si and Zr alkoxides is 1.5; PA1 mixing the fifth mixture with 1-hydroxycyclohexylphenylketone (C.sub.6 H.sub.5 COC.sub.6 H.sub.10 OH) to produce a sixth mixture containing Si/Zr alkoxides and 1-hydroxycyclohexylphenylketone (C.sub.6 H.sub.5 COC.sub.6 H.sub.10 OH) in a molar ratio of 49:1, this sixth mixture constituting the photosensitive sol-gel glass material; and PA1 filtering the sixth mixture to obtain a filtered photosensitive sol-gel glass material. PA1 the film producing step comprises dip coating a thick film of photosensitive sol-gel glass material on the substrate and pre-baking the dip coated thick film; PA1 the exposing step comprises exposing the photosensitive sol-gel glass material through the opening of the photomask to an ultraviolet light at a wavelength .lambda..ltoreq.350 nm and an intensity.apprxeq.14 W cm.sup.-2 ; PA1 the dissolving step comprises soaking the film of photosensitive sol-gel glass material in n-propanol; PA1 the step of heat curing the ridge waveguide comprises post-baking the ridge waveguide at a temperature.ltoreq.200.degree. C.; and PA1 the step of covering the heat cured ridge waveguide with a cladding layer comprises:
Only chemical vapor deposition, plasma enhanced chemical vapor deposition, flame hydrolytic deposition, and sol-gel deposition are currently employed. These different technologies have been discussed by Andrews, "An overview of sol-gel guest-host materials chemistry for optical devices", Proc. SPIE Soc. Opt. Eng. Integrated Optics devices: Potential for Commercialization, Vol. 2997, pp. 48-59 (1997).
Many of the above listed prior art technologies involve a high temperature (&gt;1000.degree. C.) glass processing incompatible with hybrid optoelectronic silicon and GaAs benches.
Regarding low temperature plasma enhanced chemical vapor deposition, this technology must entail complex multistep mask processes including reactive ion etching.
Conventional sol-gel derived glass technologies require post-film deposition thermal treatment including rapid thermal annealing at temperatures approaching or exceeding 1000.degree. C. Reactive ion etching and multistep mask technologies are required to complete the fabrication of the integrated optic device.